US5404377A - Simultaneous transmission of data and audio signals by means of perceptual coding - Google Patents

Hence, the main goal of noise shaping is to minimize the perceptibility of distortions by advantageously shaping it in time or frequency so that as many of its components as possible are masked by the audio signal itself. See Nikil Jayant et al., Signal Compression Based on Models of Human Perception, 81 Proc. of the IEEE 1385 (1993). A schematic representation of time-frequency domain masking is shown in FIGS. 1a-1c, in which a short

10 produces a

12. See John G. Beerends and Jan A. Stemerdink, A Perceptual Audio Quality Measure Based on a Psychoacoustic Sound Representation, 40 J. Audio Engineering Soc'y 963, 966 (1992).

FIGS. 1a-1c illustrate a schematic representation of time-frequency domain masking of audio distortions in which a short

10 produces a masking threshold, or perceptual entropy envelope, 12.

FIG. 2 is a schematic block diagram of an

202 embodying features of the present invention for encoding, using perceptual coding techniques, data to be transmitted simultaneously with audio signals via an audio channel (not shown), such as a television transmission channel. Perhaps most significantly, the

202 includes a multilayer, artificial neural network (NN) 204, which monitors the audio signal, via an audio-in terminal 206a, for "opportunities" to insert data signals at times, frequencies and amplitudes such that they are not perceived by human ears. In other words, the

204 determines the "perceptual entropy envelope" of the audio channel, which, as previously described, is the three dimensional (time, frequency and amplitude) map of the optimal masking function of the audio channel. It should be understood by those skilled in the art that a neural network, such as the

204, comprises a combination of simple computational elements which are "trained" to perform specific mapping tasks between input and output data. As used herein, the term "neural network" also includes any necessary preprocessing circuitry, such as filters, timing circuits and others. The mapping function of a neural network is achieved after an initial lengthy training stage during which the

204 is supplied with input and output data which satisfy the mapping task. In the present embodiment, the input data supplied to the

204 comprises segments of audio signals and the required output is the auditory noise masking threshold (i.e., the perceptual entropy envelope) created by the audio signal segments. In this manner, the

204 is "trained" to extract the perceptually significant features from the audio signal at the audio-in

218a, which relate to the perceptual entropy envelope generated by successive frames of input data. The algorithm for implementing the mapping function of the

204 is stored in a

205, which in a preferred embodiment comprises a socketed chip, to make future upgrades easy and practical.

For purposes which will subsequently be described in greater detail, the

204 controls a

208a, a

208b, and a

208c. As will also be described in detail, under the control of the

204, the data signal will be encoded as one or more whitened direct sequence spread spectrum signals and/or a narrowband FSK data signal to be combined with the audio signal a time, frequency and amplitude such that the data signal is masked by the audio signal.

A digital data signal comprising a serial number or other identification number is generated by a

210 and input to the

202, preferably via an RS232-

212, although it should be understood that any number of different types of interfaces may be used. The number generated by the

210 may be, for example, a number for identifying a television network or a local radio or television station or a number to be encoded on a compact disc (CD) for identifying a particular artist or song. The data signal output from the

210 is input to a

213 comprising a

214 for encoding the data signal to enable the detection and correction of errors therein when it is received at a decoder (FIG. 3), and a bit

216 for enabling the encoded number to withstand error hits in the transmission path. An exemplary system and method for performing such block encoding and bit interleaving techniques is described in detail in U.S. Pat. No. 4,672,605 to Hustig et al., which is hereby incorporated by reference. The data signal output from the

213 is stored in each of three random access memories (RAMs) 218a, 218b and 218c for use by a wideband

220, a bandlimited

222 and an

224, respectively, for purposes which will be described.

The wideband

220 encodes the data signal as a wideband direct sequence spread spectrum signal at processing gains and levels related to noise masking opportunities in the audio signal as determined by the

204. Specifically, the

204 dynamically determines the noise masking perceptual entropy envelope for controlling the spread spectrum processing gain (i.e., ratio of data rate to pseudo-nose (PN) code frequency rate) and the signal level of the wideband pseudo-noise transmission output from the

220. The data stored in the

218a is input to a modulo-2

228, where it is merged with a synchronous PN code from a

230 to form a direct sequence signal. In a preferred embodiment, the modulo-2

228 is implemented using an exclusive-OR (XOR) logic gate. The direct sequence signal output from the modulo-2

228 is input to a

232, which adds a PN code header signal to each frame thereof, in accordance with synchronization and timing signals from a sync and

234, in order to improve acquisition of the data signal at the decoder location(s) (FIG. 3). As shown in FIG. 2, the sync and

234 is controlled by signals from the

208c. The spectrum of the direct sequence signal output from the

232 is relatively flat over the bandwidth of the channel, as is typical of direct sequence signals in general. Once the PN code header signal has been added to each frame of the data signal, the resultant wideband spread spectrum data signal is output to a

235 via a

236, which establishes the transmit level of the signal in accordance with control signals from the level control circuit 108b, which in turn is controlled by signals from the

204.

The bandlimited

222 is similar to the wideband

220, except that it encodes the data signal as a bandlimited, rather than a wideband, direct sequence spread spectrum signal responsive to both noise masking and frequency masking opportunities in the audio channel, as determined by the

204. As with the

220, the data stored in the

218b is input to a modulo-2

238 where it is merged with a PN code from a

240 to form a direct sequence signal. The direct sequence signal output from the modulo-2

238 is input to a

242, which adds a PN code header signal to each frame thereof in accordance with synchronization and timing signals from a sync and

244. As shown in FIG. 2, the sync and

244 is controlled by signals from the

208c. As with the signal generated by the

220, the spectrum of the direct sequence signal output from the

242 is relatively flat over the bandwidth of the channel. Once the PN code header signal has been added to the direct sequence signal, the signal is output to a

246, where it is multiplied with a signal from a

248 having a high clock-to-PN code frequency. In this manner, the frequency of the signal may be raised to a selected frequency, which is preferably centered in a selected subband of the audio channel. The signal output from the

246 is then bandlimited by a

250, which translates the direct sequence signal energy into the selected subband. The resultant bandlimited spread spectrum data signal is output to the

235 via a

252, which, under the control of the

208b, controls the amplitude at which the data signal is transmitted.

The FSK burst

224 encodes the data signal as a narrowband signal which is related to time masking and frequency masking opportunities. The coded data stored in the

218c is input to a

254, which adds a header to each frame of data to facilitate acquisition of the data at the decoder location(s) (FIG. 3). The signal is then input to an

256, which FSK modulates the signal, and to a

258, which bandlimits the signal to concentrate the signal energy into a selected subband. As shown in FIG. 2, the

254 and the FSK encoder are controlled by signals from the

208c. The resultant FSK data signal is then output to the

235 via a

260, which, under the control of the

208b, controls the amplitude at which the signal is transmitted. It should be understood that the FSK data signal output from the

224 may be continuous, but dynamically varying in level, or may be in burst mode, triggered by a time masking opportunity, as determined by the

204. However, as will be described in detail, in a particular implementation in which the data signal must undergo lossy compression according to a known compression algorithm, such as MPEG, the signal must be transmitted in burst mode in order to survive such compression.

The wideband spread spectrum, bandlimited spread spectrum and FSK data signals output from the encoders 220-224, respectively, are combined by the

235 with the audio signal at the terminal 206a to form a composite signal, which is output to the audio channel at the terminal 206b. Alternatively, the composite signal may be recorded on any appropriate recording medium, such as a CD, in which case the signal will be transmitted when the CD is "played back." In a preferred embodiment, as illustrated in FIG. 2, before being input to the

235, the audio signal is input to a device, such as a digital signal processor (DSP) 260a, which, under the control of signals from the

204, functions to attenuate the level of the audio signal in certain subbands. Such attenuation might be necessary, for example, if the

204 signals an FSK burst or bandlimited spread spectrum signal transmission and then detects an unexpected burst of energy in the subband of the audio signal that would interfere with the data transmission. The composite signal is also input to a

261 comprising a

262, which adds noise to and degrades the composite signal slightly more than would be typical during transmission over the actual audio channel, and a

264. The ability of the

264 successfully to decode the data information contained in the composite signal is verified and a verification signal is transmitted to the

204.

It should be obvious that if perceptual coding techniques such as those described above are used to encode the data signal to be transmitted, then perceptual compression schemes, such as MPEG and PASC, will most likely remove the data from the composite signal before or during transmission. Therefore, to overcome this problem, the

204 must be trained not only to listen to the channel for opportunities at which the data signal may be transmitted imperceptibly, but also to compensate for the particular compression scheme to be encountered.

For example, one well-known and widely used compression scheme divides the audio band into thirty-two (32) subbands. Taking advantage of frequency domain masking, and to a certain extent, time domain masking, only the strongest signal in each subband is encoded and transmitted on the assumption that the remaining signals in the subband would not be heard anyway, as they would be masked by the stronger signal. In this case, in order to ensure that the data signal is transmitted, the

204 must be trained to "listen" for opportunities to transmit the data signal as an FSK burst signal where the data signal will be the strongest signal in a particular subband, with its transmission masked by following strong, broadband transients (time domain masking) in proximate subbands.

FIG. 3 is a schematic block diagram of a

300 embodying features of the present invention for retrieving (i.e., decoding) data signals encoded using the

202 and transmitted via the audio channel. The

300 receives the composite signal transmitted via the audio channel (not shown) at an audio-in

302. The received signal is input to a

304, the parameters of which are defined by the passband of the audio channel, for filtering out any unnecessary frequencies. The signal output from the

304 is input to a

305 comprising an automatic gain controller (AGC) 306, which maintains the amplitude of the signal within an acceptable range, an

308, which compensates for known phase and amplitude distortions in the signal path, and an analog-to-digital (A/D) converter 310, which converts the signal to digital form to facilitate processing. The digital signal output from the

305 is input to a

312 and to an FSK

314.

The

312 performs sync acquisition of the wideband and/or bandlimited spread spectrum signals in quadrature phase using an iterative phase stepping procedure, as hereinafter described. A header PN code identical to that generated by the

232, 242 (FIG. 1) is generated by a

316 and merged modulo-2 with the signal output from the

305, in quadrature phase, in a wide dynamic range (i.e.. 18- to 24-bits of resolution) digital signal processor (DSP) 318. In the illustrated embodiment, the

318 comprises four

318a-318d. Four signals output from the

318 are input to a lock detect

320 for detecting when the phase of the data signal is locked with that of the header PN code from the

316. A signal indicative of whether a phase lock has been detected is input to a

322 and a digital

324. So long as the signal output from the

320 indicates that the phase of the signal has not been locked onto, the phase shift circuit continues to shift the phase until the

320 detects a phase lock. It should be understood that typically, lock will occur in bursts, when the data transmitted is received with the highest quality. For this reason, the

324 operates as a flywheel, retaining clock phase sync between bursts of lock.

Clock signals generated by the

324 are fed to a

326 of a

328. The PN code is merged modulo-2 with the signal output from the

305 by an

330 to recover the data signal containing the ID number. The output of the

330 will typically be a fuzzy logic set, because, as previously indicated, transmission of the data usually occurs in a partial response mode. The signal output from the

330 is input to a neural network (NN) 332, which in a preferred embodiment comprises a "back propagation perceptron" that uses pattern and signature recognition techniques to perform block decoding, bit deinterleaving and acquisition confirm functions. As such pattern and signature recognition techniques and backpropagation perceptrons for implementing same are well known in the art they will not be further described.

Once acquisition of the data signal/ID number is confirmed by the

332, using pattern recognition, this fact is indicated to the lock detect

320 as confirmation that the lock is valid. The decoded ID number is then output from the

332 after a relatively long delay, for example, ten seconds. Alternatively, the signal output from the

332 may simply indicate that the decoded number is the same as the previous number, that the decoded number is indeterminate, or that the decoded number is different than the previous number, in which case the new decoded number is output as described above. The ID numbers output from the

332 is held in a data storage unit (DSU) 334, the contents of which may be transferred at regular intervals by any appropriate means to a central processing unit (not shown), which processes the recovered ID numbers such that they may be used, for example, in performing radio and television surveys, as well as music royalty tracking applications, as described below.

Referring again to the

314, to decode data transmitted as an FSK burst signal, the signal output from the

305 is input to a

336, similar to the

258, and then to an

338 for decoding the signal. Again, because data transmission occurs in a partial response environment, the output of the

338 will be a fuzzy logic set. The fuzzy logic signal output from the

338 is input to the

332, which processes the signal in the same manner as signals input thereto from the

330.

FIGS. 4a-4e illustrate various frequency and timing diagrams of exemplary data and audio signals used and/or produced by the system of the present invention. FIG. 4a illustrates the energy of an

400, such as that which might be received at the audio in terminal 206a, with respect to frequency. FIG. 4b is a timing diagram of the voltage of a

410 of the

400 within a selected subband 402 (FIG. 4a). FIG. 4c is a timing diagram of the energy of the

410 within the

402. Also shown in FIG. 4c is a

420 of the

410, as well as the

422 thereof, it being understood that the

410 will mask signals having signal energy below its

422. FIG. 4d illustrates a

430, such as that which might be encoded by the

202, to be transmitted with and masked by the

410. It should be noted that the data signal 430 occurs as a burst signal which undergoes exponential decay for 100 ms. FIG. 4e is a timing diagram of a

440, such as that which might be output from the

202 via the audio out terminal 206b, comprising the

410 and the data signal 430.

In operation, it is anticipated that the above-described invention may be advantageously used for several purposes, which include, but are not limited to, television and radio surveys and music royalty tracking. For example, in television and radio survey applications, the audio signal at the terminal 206a comprises programming signals and the data signal comprises ID codes for identifying the local station, the broadcaster, the distributor, and others, as well as codes for identifying certain programming and advertisements, may be encoded, as described above, transmitted with the television or radio audio signal, and received at an encoder located in a television viewer or radio listeners home or at some central location. The decoded ID code(s) may then be used to determine the size of the audience for a particular program or time slot at any given time. In a music royalty tracking application, it is envisioned that encoded ID numbers be recorded on CDs such that when the CD is played, the data signal containing the ID code identifying the music programming is transmitted with the audio signal recorded thereon. Again, the encoded data signal may be received and decoded at various strategically located decoding locations having a

300. Typically, this technique will be used to collect data for collecting royalties for computing ratings, such as the "Billboard Top 100".

It is understood that the present invention can take many forms and embodiments. The embodiments shown herein are intended to illustrate rather than to limit the invention, it being appreciated that variations may be made without departing from the spirit of the scope of the invention. For example, the encoder 200 may comprise fewer than all of the transmission encoders 220-224, especially if it is known prior to transmission of the data signal that the data signal will or will not have withstand lossy compression. In addition, the functions of any of the

220, 222, 224, as well as those of the

314, and the

328/

314 combination may be performed by digital signal processors, if desired.

1. Apparatus for encoding a data signal to be transmitted simultaneously with an audio signal such that said encoded data signal is masked by said audio signal, the apparatus comprising:

means for monitoring said audio signal to determine a perceptual entropy envelope thereof, said monitoring means generating control signals indicative of said determined perceptual entropy envelope;

means responsive to said control signals for encoding said data signal as an frequency shift key (FSK) modulated signal and for outputting said FSK modulated signal at times, frequencies and levels falling within said determined perceptual entropy envelope of said audio signal such that when combined with said audio signal, said FSK modulated signal is masked by said audio signal; and

means for combining said audio signal with said FSK modulated signal to form a composite signal.

2. The apparatus of claim 1 further comprising means responsive to said control signals for encoding said data signal as a spread spectrum signal and for outputting said spread spectrum signal at times, frequencies and levels falling within said detected perceptual entropy envelope of said audio signal such that when combined with said audio signal, said transmitted spread spectrum signal is masked by said audio signal, wherein said means for combining further combines said spread spectrum signal with said FSK modulated signal and said audio signal.

3. The apparatus of claim 2 wherein said spread spectrum encoding means comprises:

means for merging said data signal modulo-2 with a pseudo noise (PN) code; and

means for adding a PN header signal to each frame of said data signal.

4. The apparatus of claim 1 wherein said monitoring means comprises an artificial neural network.

5. The apparatus of claim 4 wherein said monitoring means further comprises:

a clock control circuit connected to an first output of said neural network for generating control signals to control the transmission frequency of said encoded data signal;

a level control circuit connected to an second output of said neural network for generating control signals to control the level of said encoded data signal; and

a burst timing circuit connected to an third output of said neural network for generating control signals to control the timing of transmission of said encoded data signal.

6. The apparatus of claim 1 wherein said monitoring means comprises means for determining the perceptual entropy envelope of said audio signal only in a first group of subbands, wherein each subband in said first group of subbands is proximate to a selected subband, said determining means generating control signals to said FSK modulating means for causing said FSK modulating means to output said FSK modulated signal in said selected subband such that it is masked by said audio signal in at least one subband in said first group of subbands and such that it is the strongest signal in said selected subband.

7. The apparatus of claim 1 wherein said data signal contains information for identifying at least one of a broadcaster, a program, a network, or an advertiser.

8. The apparatus of claim 1 further comprising:

means for generating said data signal;

means connected to receive said data signal from said generating means for encoding said data signal to withstand error hits during transmission using bit interleaving and block encoding techniques and for supplying said data signal to said FSK encoding means.

9. The apparatus of claim 1 further comprising means for transmitting said composite signal via an audio channel.

10. The apparatus of claim 1 further comprising means for recording said composite signal on a data storage medium.

11. Apparatus for encoding a data signal to be transmitted simultaneously with an audio signal such that said data signal is masked by said audio signal, the apparatus comprising:

means for monitoring said audio signal to determine a perceptual entropy envelope thereof, said monitoring means generating control signals indicative of said determined perceptual entropy envelope;

means responsive to said control signals for encoding said data signal as a spread spectrum signal and for outputting said spread spectrum signal at times, frequencies and levels falling within said determined perceptual entropy envelope of said audio signal such that when combined with said audio signal, said spread spectrum signal is masked by said audio signal; and

means for combining said audio signal with said spread spectrum signal to form a composite signal.

12. The apparatus of claim 11 wherein said encoding means comprises:

means for merging said data signal modulo-2 with a pseudo noise (PN) code; and

means for adding a PN header signal to each frame of said data signal.

13. The apparatus of claim 11 further comprising means responsive to said control signals for frequency shift key (FSK) modulating said data signal and for outputting said FSK modulated signal at times, frequencies and levels falling within said detected perceptual entropy envelope of said audio signal such that when combined with said audio signal, said FSK modulated signal is masked by said audio signal, wherein said means for combining further combines said spread spectrum signal with said spread spectrum signal and said audio signal.

14. The apparatus of claim 11 wherein said monitoring means comprises an artificial neural network.

15. The apparatus of claim 14 wherein said monitoring means further comprises:

a clock control circuit connected to an first output of said neural network for generating control signals to control the transmission frequency and processing gain of said spread spectrum signal;

a level control circuit connected to an second output of said neural network for generating control signals to control the level of said spread spectrum signal; and

a burst timing circuit connected to an third output of said neural network for generating control signals to control the timing of transmission of said spread spectrum signal.

16. The apparatus of claim 11 further comprising:

means for generating said data signal;

means connected to receive said data signal from said generating means for encoding said data signal to withstand error hits during transmission using block encoding and bit interleaving techniques and for supplying said data signal to said FSK modulation means.

17. The apparatus of claim 11 wherein said data signal contains information for identifying at least one of a broadcaster, a program, a network, or an advertiser.

18. Apparatus for decoding a data signal containing an information code transmitted simultaneously with an audio signal such that said data signal is masked by said audio signal, wherein prior to transmission, said data signal is encoded as frequency shift key (FSK) modulated signal, a direct sequence spread spectrum (DSSS) signal or both, said encoded data signal being combined with said audio signal to form a composite signal, the apparatus comprising:

means for receiving said composite signal from an audio channel;

means connected to said receiving means for filtering said received composite signal, wherein passband parameters of said filtering means are dictated by the bandwidth of said audio channel;

means connected to an output of said filtering means for demodulating said FSK modulated signal if said encoded data signal comprises an FSK modulated signal; and

means connected to said filtering means output for decoding said DSSS signal if said encoded data signal comprises a DSSS signal.

19. The decoder of claim 18 wherein said encoded data signal is transmitted in a partial response mode and first and second fuzzy logic forms of said data signal are output from said FSK demodulating means and said DSSS decoding means, respectively, the decoder further comprising means connected to an output of said FSK demodulating means and to an output of said DSSS decoding means for recovering said information code from said first and second fuzzy logic data signals using pattern recognition techniques.

20. The apparatus of claim 18 wherein said means for decoding said DSSS signal comprises:

means for synchronizing the phase of a clock signal with the phase of said DSSS signal and for outputting said synchronized clock signal; and

means connected to receive said synchronized clock signal for merging said DSSS signal modulo-2 with a pseudo-noise (PN) code used to encode the data signal.

21. The apparatus of claim 18 further comprising a data storage unit connected to an output of said FSK demodulating means and to an output of said DSSS decoding means.

22. The apparatus of claim 19 further comprising a data storage unit connected to an output of said recovering means for temporarily storing said recovered information code.

23. The apparatus of claim 19 wherein said recovering means comprises an artificial neural network.

24. A communications system for enabling the simultaneous transmission of a data signal and an audio signal via an audio channel such that said data signal is masked by said audio signal, the system comprising:

means for monitoring said audio signal to determine a perceptual entropy envelope thereof, said monitoring means generating control signals indicative of said determined perceptual entropy envelope;

means responsive to said control signals for encoding said data signal as an frequency shift key (FSK) modulated signal and for outputting said FSK modulated signal at times, frequencies and levels falling within said determined perceptual entropy envelope of said audio signal such that when combined with said audio signal, said FSK modulated signal is masked by said audio signal;

means responsive to said control signals for encoding said data signal as a spread spectrum signal and for outputting said spread spectrum signal at times, frequencies and levels falling within said determined perceptual entropy envelope of said audio signal such that when combined with said audio signal, said spread spectrum signal is masked by said audio signal;

means for combining said audio signal, said FSK modulated signal and said spread spectrum signal to form a composite signal;

means for transmitting said composite signal via said audio channel;

means for receiving said transmitted composite signal from said audio channel;

means connected to said receiving means for demodulating said FSK modulated signal of said received composite signal;

means connected to said receiving means for decoding said spread spectrum signal of said received composite signal; and

means connected to an output of said demodulating means and to an output of said decoding means for recovering an information code from said demodulated FSK signal and said decoded spread spectrum signal using pattern recognition techniques.

25. The system of claim 24 wherein said encoded data signal is transmitted in a partial response mode, such that said FSK demodulating means and said DSSS decoding means output first and second fuzzy logic forms of said data signal, respectively, the system further comprising means connected to outputs of said FSK demodulating means and said DSSS decoding means for recovering said information code from said first and second fuzzy logic data signals using pattern recognition techniques.

26. The system of claim 24 further comprising means connected to said receiving means for filtering said received composite signal, wherein the passband parameters of said filtering means are dictated by the bandwidth of said audio channel.

27. The system of claim 24 wherein said monitoring means comprises an artificial neural network.

28. The system of claim 27 wherein said monitoring means further comprises:

a clock control circuit connected to an first output of said neural network for generating control signals to control the transmission frequency and processing gain of said FSK modulated signal and said spread spectrum signal;

a level control circuit connected to an second output of said neural network for generating control signals to control the level of said FSK modulated signal and said spread spectrum signal; and

a burst timing circuit connected to an third output of said neural network for generating control signals to control the timing of transmission of said FSK modulated signal and said spread spectrum signal.

29. The system of claim 24 wherein said monitoring means comprises means for determining the perceptual entropy envelope of said audio signal only in a first group of subbands, wherein each subband in said first group of subbands is proximate to a selected subband, said determining means generating control signals to said FSK modulating means for causing said FSK modulating means to output said FSK modulated signal in said selected subband such that it is masked by said audio signal in at least one subband in said first group of subbands and such that it is the strongest signal in said selected subband.

30. The system of claim 24 further comprising:

means for generating said data signal;

means connected to receive said data signal from said generating means for encoding said data signal to withstand error hits during transmission using bit interleaving and block encoding techniques and for supplying said data signal to said FSK encoding means.

31. The system of claim 24 wherein said spread spectrum encoding means comprises:

means for merging said data signal modulo-2 with a pseudo noise (PN) code; and

means for adding a PN header signal to each frame of said data signal.

32. The system of claim 24 wherein said means for decoding said DSSS signal comprises:

means for synchronizing the phase of a clock signal with the phase of said DSSS signal and for outputting said synchronized clock signal; and

means connected to receive said synchronized clock signal for merging said DSSS signal modulo-2 with said pseudo-noise (PN) code.

33. The system of claim 24 wherein said recovering means comprises an artificial neural network.

34. The system of claim 24 further comprising a data storage unit connected to an output of said recovering means for temporarily storing said information code.

35. The system of claim 24 wherein said data signal contains information for identifying at least one of a broadcaster, a program, a network, or an advertiser.

36. A method of encoding a data signal to be transmitted simultaneously with an audio signal such that said encoded data signal is masked by said audio signal, the method comprising:

monitoring said audio signal to determine a perceptual entropy envelope thereof;

generating control signals indicative of said determined perceptual entropy envelope;

responsive to said control signals, encoding said data signal as an frequency shift key (FSK) modulated signal;

outputting said FSK modulated signal at times, frequencies and levels falling within said determined perceptual entropy envelope of said audio signal such that when combined with said audio signal, said FSK modulated signal is masked by said audio signal; and

combining said audio signal with said FSK modulated signal to form a composite signal.

37. The method of claim 36 further comprising:

responsive to said control signals, encoding said data signal as a spread spectrum signal; and

outputting said spread spectrum signal at times, frequencies and levels falling within said determined perceptual entropy envelope of said audio signal such that when combined with said audio signal, said spread spectrum signal is masked by said audio signal;

wherein said combining further comprises combining said spread spectrum signal with said FSK modulated signal and said audio signal.

38. The method of claim 37 wherein said spread spectrum encoding comprises:

merging said data signal modulo-2 with a pseudo noise (PN) code; and

adding a PN header signal to each frame of said data signal.

39. The method of claim 36 wherein said generating comprises:

generating control signals to control the transmission frequency of said encoded data signal;

generating control signals to control the level of said encoded data signal; and

generating control signals to control the timing of transmission of said encoded data signal.

40. The method of claim 36 wherein said monitoring further comprises:

determining the perceptual entropy envelope of said audio signal only in a first group of subbands, wherein each subband in said first group of subbands is proximate to a selected subband; and

generating control signals to said FSK modulating means for causing said FSK modulating means to output said FSK modulated signal in said selected subband such that it is masked by said audio signal in at least one subband in said first group of subbands and such that it is the strongest signal in said selected subband.

41. The method of claim 36 further comprising:

generating said data signal;

encoding said data signal to withstand error hits during transmission using bit interleaving and block encoding techniques prior to said FSK encoding.

42. The method of claim 36 further comprising transmitting said composite signal via an audio channel.

43. The method of claim 36 further comprising recording said composite signal on a data storage medium.

44. The method of claim 36 wherein said monitoring is performed by an artificial neural network.

45. The method of claim 36 wherein said data signal contains information for identifying at least one of a broadcaster, a program, a network, or an advertiser.

46. A method of encoding a data signal to be transmitted simultaneously with an audio signal such that said data signal is masked by said audio signal, the method comprising:

monitoring said audio signal to determine a perceptual entropy envelope thereof;

responsive to said monitoring, generating control signals indicative of said determined perceptual entropy envelope;

responsive to said control signals, encoding said data signal as a spread spectrum signal;

outputting said spread spectrum signal at times, frequencies and levels falling within said determined perceptual entropy envelope of said audio signal such that when combined with said audio signal, said spread spectrum signal is masked by said audio signal; and

combining said audio signal with said spread spectrum signal to form a composite signal.

47. The method of claim 46 wherein said encoding comprises:

merging said data signal modulo-2 with a pseudo noise (PN) code; and

adding a PN header signal to each frame of said data signal.

48. The method of claim 46 further comprising, responsive to said control signals, frequency shift key (FSK) modulating said data signal and for outputting said FSK modulated signal at times, frequencies and levels falling within said determined perceptual entropy envelope of said audio signal such that when combined with said audio signal, said FSK modulated signal is masked by said audio signal, wherein said means for combining further combines said spread spectrum signal with said spread spectrum signal and said audio signal.

49. The method of claim 43 wherein said monitoring further comprises:

generating control signals to control the transmission frequency and processing gain of said spread spectrum signal;

generating control signals to control the level of said spread spectrum signal; and

generating control signals to control the timing of transmission of said spread spectrum signal.

50. A method of decoding a data signal containing an information code transmitted simultaneously with an audio signal such that said data signal is masked by said audio signal, wherein prior to transmission, said data signal is encoded as frequency shift key (FSK) modulated signal, a direct sequence spread spectrum (DSSS) signal or both, said encoded data signal being combined with said audio signal to form a composite signal, the method comprising:

receiving said composite signal from an audio channel;

filtering said received composite signal, wherein passband parameters of said filtering are dictated by the bandwidth of said audio channel;

demodulating said FSK modulated signal if said encoded data signal comprises an FSK modulated signal; and

decoding said DSSS signal if said encoded data signal comprises a DSSS signal.

51. The method of claim 50 wherein said encoded data signal is transmitted in partial response mode, said FSK demodulating and said DSSS decoding produce first and second fuzzy logic forms of said data signal, respectively, the method further comprising recovering said information code from said first and second fuzzy logic data signals using pattern recognition techniques.

52. The method of claim 50 further comprising temporarily storing said recovered information code.

53. The method of claim 50 wherein said decoding said DSSS signal comprises:

synchronizing the phase of a clock signal with the phase of said DSSS signal and outputting said synchronized clock signal; and

merging said DSSS signal modulo-2 with a pseudo-noise (PN) code used to encode the data signal.

54. A method of enabling the simultaneous transmission of a data signal and an audio signal via an audio channel such that said data signal is masked by said audio signal, the method comprising:

monitoring said audio signal to determine a perceptual entropy envelope thereof, said monitoring means generating control signals indicative of said determined perceptual entropy envelope;

responsive to said control signals, encoding said data signal as an frequency shift key (FSK) modulated signal and outputting said FSK modulated signal at times, frequencies and levels falling within said determined perceptual entropy envelope of said audio signal such that when combined with said audio signal, said FSK modulated signal is masked by said audio signal;

responsive to said control signals, encoding said data signal as a spread spectrum signal and outputting said spread spectrum signal at times, frequencies and levels falling within said determined perceptual entropy envelope of said audio signal such that when combined with said audio signal, said spread spectrum signal is masked by said audio signal;

combining said audio signal, said FSK modulated signal and said spread spectrum signal to form a composite signal;

transmitting said composite signal via said audio channel;

receiving said transmitted composite signal from said audio channel;

demodulating said FSK modulated signal of said received composite signal;

decoding said spread spectrum signal of said received composite signal; and

recovering an information code from said demodulated FSK modulated signal and said decoded spread spectrum signal using pattern recognition techniques.

55. The method of claim 54 further comprising filtering said received composite signal, wherein passband parameters of said filtering are dictated by the bandwidth of said audio channel.

56. The method of claim 54 wherein said spread spectrum encoding comprises:

merging said data signal modulo-2 with a pseudo noise (PN) code; and

adding a PN header signal to each frame of said data signal.

57. The system of claim 54 wherein said monitoring further comprises:

determining the perceptual entropy envelope of said audio signal only in a first group of subbands, wherein each subband in said first group of subbands is proximate to a selected subband; and

responsive to said determining, generating control signals to said FSK modulating means for causing said FSK modulating means to output said FSK modulated signal in said selected subband such that it is masked by said audio signal in at least one subband in said first group of subbands and such that it is the strongest signal in said selected subband.

58. The method of claim 54 further comprising temporarily storing said information code.

59. The system of claim 54 wherein said decoding said spread spectrum signal comprises:

synchronizing the phase of a clock signal with the phase of said spread spectrum signal and outputting said synchronized clock signal; and

merging said DSSS signal modulo-2 with said pseudo-noise (PN) code.